Empty elements in EMACSLOADPATH now stand for the default

* src/lread.c (load_path_check): Take path to check as argument.
(load_path_default): New, split from init_lread.
(init_lread): Move calc of default load-path to load_path_default.
Empty elements in EMACSLOADPATH now stand for the default.
(load-path): Doc fix.

* src/emacs.c (decode_env_path): Add option to treat empty elements
as nil rather than ".".

* src/callproc.c (init_callproc_1, init_callproc):
* src/image.c (Vx_bitmap_file_path):
* src/lisp.h (decode_env_path):
* lread.c (Vsource_directory):
Update for new argument spec of decode_env_path.

* leim/Makefile.in (RUN_EMACS): Empty EMACSLOADPATH rather than unsetting.

* lisp/Makefile.in (emacs): Empty EMACSLOADPATH rather than unsetting.

* test/automated/Makefile.in (emacs):
Empty EMACSLOADPATH rather than unsetting.

* doc/emacs/cmdargs.texi (General Variables):
Empty elements in EMACSLOADPATH now mean the default load-path.

* doc/lispref/loading.texi (Library Search):
Empty elements in EMACSLOADPATH now mean the default load-path.

* etc/NEWS: Mention this.

Fixes: debbugs:12100

1 files changed, 10 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 97ae6c79d20..4dc1543d845 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -63,6 +63,16 @@ To use the old backend by default, do on the command line:
 * Startup Changes in Emacs 24.4
 
 +++
+** When initializing `load-path', an empty element in the EMACSLOADPATH
+environment variable (either leading, e.g., ":/foo"; trailing, e.g.,
+"/foo:"; or embedded, e.g., "/foo::/bar") is replaced with the default
+load-path (the one that would have been used if EMACSLOADPATH was unset).
+This makes it easier to _extend_ the load-path via EMACSLOADPATH
+(previously, EMACSLOADPATH had to specify the complete load-path,
+including the defaults).  (In older versions of Emacs, an empty element
+was replaced by ".", so use an explicit "." now if that is what you want.)
+
++++
 ** The -L option, which normally prepends its argument to load-path,
 will instead append, if the argument begins with `:' (or `;' on MS Windows;
 i.e., `path-separator').